1. Technical Field to Which the Invention Belongs
This invention relates to flow-and-leveling agents for paints and inks, which, when added to paints and inks in minor amounts, can impart to the paints and inks flow-and-leveling property in the occasions of their application or printing and at the same time can prevent occurrence of coating or printing defects even in the presence of foreign matters which are a cause of ruptures in coating or printing step.
2. Prior Art
Paints which are applied by industrial line operation, such as those high quality paints for automotives, precoat metal (PCM) paints and paints for household appliances, are required to exhibit not only anti-corrosion property but also high quality finish excelling in appearance. It is, therefore, essential that the finished surfaces are free from cissing, cratering, fish-eyes, clouds and the like and are level and smooth. As paint additives for imparting such functions, surface control agents such as flow-and-leveling agents, defoamers, anti-popping agents, brighteners and anti-rupture agents are used.
Conventionally, atomizing coating such as air spray or high-speed continuous coating using roll coater or the like have been practiced in line coating. According to these coating methods, mist of the lubricants used on compressors, roll coater machines and the like or mist of the used paints may deposit on the surfaces of the objects being painted and cause occurrence of ruptures. Besides this problem, in coating lines wherein coating and sanding are repeated plural times as in the case of coating automobile bodies, ruptures caused by dust formed during sanding with sand paper or soiling with operators""hands can create a problem. (These matters which can cause ruptures are hereafter collectively referred to as xe2x80x9cforeign dustxe2x80x9d).
As a means to solve this problem of ruptures at the coating time, heretofore modified silicone oils or vinyl ether polymers have been used as additives. For example, Japanese Patent Publication Hei 1 (1989)-234478B1 taught the usefulness of vinyl ether polymers having C2-C4 alkyl groups as anti-rupture agent.
Recently high-solid paints for environmental preservation or paints free of melamine resin curing agents to cope with acid precipitation are commercialized. When modified silicone oils or vinyl ether polymers are added to those recently marketed paints, however, they tend to adversely affect re-coating property of those paints (i.e., interlayer-adherability of over-painted layers is impaired or color tone of top coating is changed).
Accordingly, therefore, the object of the present invention is to provide flow-and-leveling agents which prevent ruptures caused by foreign dust and give smooth and level painted surfaces, without interfering with the paints"" recoating property.
As a result of various studies, we have come to discover that the above object of the invention is accomplished by blending a flow-and-leveling agent comprising a copolymer having a number-average molecular weight of 1,000-60,000, preferably 2,000-30,000 with paints, said copolymer being formed by copolymerizing
2-50% by weight, preferably 5-35% by weight of silicone oil containing an acryloyloxy group or methacryloyloxy group, as monomer (A) which is expressed by the following general formula (I): 
in which R1 stands for hydrogen or methyl,
R2 stands for C1-C10 alkylene,
R3 stands for C1-C4 alkyl, and
n stands for an integer of 5-100,
with
50-98% by weight, preferably 65-95% by weight, of an acrylic acid ester or methacrylic acid ester as monomer(B) of the following general formula (II): 
xe2x80x83in which R4 stands for hydrogen or methyl, and
R5 stands for C1-C12 alkyl
and/or an acrylic acid ester or methacrylic acid ester as monomer (C) of the following general formula (II) 
in which R6 stands for hydrogen or methyl,
R7 stands for hydrogen or C1-C18 alkyl,
n stands for an integer of 2-4, and
m stands for an integer of 1-50.
We have also discovered that the object of the present invention could equally be accomplished by blending a flow-and-leveling agent with paints, said agent comprising a copolymer having a number-average molecular weight of 1,000-60,000, preferably 2,000-30,000, which is formed by copolymerizing with said monomer (A) and monomer (B) and/or monomer (C), still another monomer (D), which has a polymerizable double bond and is copolymerizable with said monomers, of an amount not exceeding 50% by weight based on the total weight of said monomers (A) and (B) and/or (C).
Where the amount of monomer (A) is less than 2% by weight, sufficient anti-rupture effect cannot be recognized. Whereas, when it exceeds 50% by weight, re-coating property of the paint is adversely affected.
Those specific (meth)acrylic acid esters [monomer (B) and/or monomer (C)] are used as the copolymerizing components in an amount of 50-98% by weight, for securing favorable flow-and-leveling property. Use of monomers other than those cannot impart sufficient flow-and-leveling property to the paints. When the degree of polymerization (m) of the polyalkylene glycol as monomer (C) exceeds 50, not only satisfactory flow-and-leveling property cannot be expected, but also physical properties of painted films are liable to be adversely affected. Where monomers (B) and (C) are concurrently used, their quantitative ratio is optional, so long as their sum falls within the range of 50-98% by weight of the copolymer.
Those copolymers formed of monomer (A) and monomer (B) and/or monomer (C) and monomer (D) can impart good flow-and-leveling property and anti-rupture property, similarly to said two- or three-component copolymers, so long as the use ratio of the monomer (D) is within the specified ratio.
Where the number-average molecular weight of the copolymer is less than 1,000 or more than 60,000, sufficient flow-and-leveling property cannot be obtained by blending it with paints, because its orientability on the painted surfaces at the coating time is insufficient.
Examples of said silicone oil (monomer A) represented by the general formula (I), which has an acryloyloxy group or a methacryloyloxy group include reactive silicones having methacryloyloxy groups (Silaplane(trademark) FM-0711, FM-0721 and FM-0725, Chisso Corporation; AK-5 and AK-30, Toagosei Co., Ltd.).
Examples of (meth)acrylic acid esters (monomer B) represented by the general formula (II) include: methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, i-propyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, tert-butyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isononyl (meth)acrylate and lauryl (meth)acrylate.
Examples of said (meth)acrylic acid esters (monomer C) represented by the general formula (III) include: 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, 2-butoxyethyl (meth)acrylate, 2-octoxyethyl (meth)acrylate, 2-lauroxyethyl (meth)acrylate, 3-methoxybutyl (meth)acrylate, 4-methoxybutyl (meth)acrylate, ethylcarbitol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate (in which the degree of polymerization of ethylene glycol is 2-50), methoxypolypropylene glycol (meth)acrylate (in which the degree of polymerization of propylene glycol is 2-50), methoxy-poly (ethylene-propylene) glycol (meth)acrylate (in which the degree of polymerization of ethylene glycol-propylene glycol is 2-50), methoxy-poly (ethylene-tetramethylene) glycol (meth)acrylate (in which the degree of polymerization of ethylene glycol-tetramethylene glycol is 2-50), butoxy-poly (ethylene-propylene) glycol (meth)acrylate (in which the degree of polymerization of ethylene glycol-propylene glycol is 2-50), octoxy-poly (ethylene-propylene) glycol (meth)acrylate (in which the degree of polymerization of ethylene glycol-propylene glycol is 2-50), and lauroxy-polyethylene glycol (meth)acrylate (in which the degree of polymerization of ethylene glycol is 2-50).
A copolymer according to the present invention may contain up to 50% by weight, based on the total weight of those segments composed of the monomers A, B and/or C, of monomer D segments. Said monomer D is subject to no limitation, examples of which include (meth)acrylic acid; (meth)acrylic acid esters other than the monomers (B) and (C), such as stearyl (meth)acrylate, cyclohexyl (meth)acrylate, benzyl (meth)acrylate and phenoxyethyl (meth)acrylate; acrylamides such as acrylamide, N,N-dimethylacrylamide, N,N-diethylacrylamide, N-isopropylacrylamide, diacetoneacrylamide and acroylmorpholine; aromatic vinyl compounds such as styrene, xcex1-methylstyrene, chlorostyrene and vinyltoluene; vinyl esters such as vinyl acetate and vinyl propionate; allyl compounds such as diallyl phthalate; vinyl ethers such as ethyl vinyl ether, n-propyl vinyl ether, iso-propyl vinyl ether, n-butyl vinyl ether, iso-butyl vinyl ether, tert-butyl vinyl ether, n-octyl vinyl ether, 2-ethylhexyl vinyl ether, 2-hydroxyethyl vinyl ether, methyl vinyl ether and cyclohexyl vinyl ether; and other vinyl compounds such as vinyl chloride, vinylidene chloride, chloroprene, propylene, butadiene, isoprene and fluoroolefin maleimide.
As the method for synthesizing the copolymers, for example, emulsion polymerization, suspension polymerization, solution polymerization and block polymerization may be named, and as initiators for the polymerization, commonly used azo polymerization initiators or peroxides are useful. The present invention concerns a function of the copolymers, and is free of any limitation incurred by methods of synthesizing the copolymers.
Paints and inks to which the flow-and-leveling agent of the present invention can be suitably added are those to which high quality appearance is required and hence ruptures caused by foreign dust therein creates problems. For example, top coating paints for automobiles comprising acid catalyst-curing type acrylic melamine paints, acid-epoxy curing type acrylic paints and baked finish-type polyester melamine paints; paints for high-quality finished appearance composed chiefly of household appliance PCM; paints for automobile repairing or high class household furnitures, using ambient temperature-drying paints such as fluorine-containing resin paints, acrylic urethane paints and polyester urethane paints. Those paints come to exhibit anti-rupture property, i.e., resistance to ruptures caused by foreign dust, as well as flow-and-leveling property, upon being blended with the flow-and-leveling agent according to the present invention.
The time for addition of the flow-and-leveling agent of the present invention to paints or inks is optional. It may be added in the grinding process, or to finished paints or inks.
The use rate of the flow-and-leveling agent is variable depending on the kind or type of individual paints and inks, composition of pigment formulations and the like. Whereas, normally it is 0.01-5% by weight, preferably 0.5-2% by weight, to the vehicle, as converted to solid.
Where the use rate is less than 0.01% by weight, preventive effect of ruptures caused by foreign dust is not achieved and flow-and-leveling property cannot be sufficiently exhibited. On the other hand, when more than 5% by weight is added, liability to adversely affect defoaming property or to impair re-coating performance increases.
The flow-and-leveling agent for paints and inks according to the invention can effectively prevent deterioration in appearance of painted or printed surfaces attributable to ruptures caused by foreign dust and at the same time impart flow-and-leveling property to the painted or printed surfaces.